The present invention relates to a reliable and low-cost semiconductor device, or more in particular to an IC (Integrated Circuit) card or a multichip module.
Conventional techniques for IC cards are described in "Information Processing Handbook", first edition, pp. 302-304, compiled by Information Processing Society of Japan and published by Ohm, May 30, 1989. The same reference contains at pp. 242-244 also the description of techniques for packaging the IC card. The structure of IC cards is described in "IC Cards", first edition, p. 33, compiled by The Institute of Electronics, Information and Communication Engineers and published by Ohm, May 25, 1990. Also, an IC card using a thin LSI is disclosed in JP-A-3-87299, Apr. 12, 1991.
FIGS. 1, 2 and 3 are sectional views showing configurations of IC cards.
In FIG. 1 showing a conventional IC card configuration, a chip 211 is bonded to a portion having a contact 210, connected to a printed board 212 by a bonding wire 216, and sealed by resin 215. This module is embedded in a center core 213 of a hard material. The card surface is covered with an oversheet 209 and an oversheet 214.
FIG. 2 shows another example of the prior art. A semiconductor chip is bonded to a substrate 207 by a adhesive agent 207a. Due to a thick silicon substrate 217, however, the semiconductor is connected by being bonded to the substrate 207 by the adhesive 207a while absorbing the unevenness through a bonding wire 218.
In the example shown in FIG. 3, an IC 6 has a great thickness of about 200 to 400 .mu.m. This bulk IC 6 is bonded to a card board 8 by an adhesive 7. Since the bulk IC is thick, however, the uneven wiring patterns on the IC and a substrate wiring 10 are connected by a wire bonding 9. In this case, the bulk IC is easily subjected to bending stress and therefore stress relaxation is required. Also, in view of the limited sizes of the bulk IC, the structural requirement for improving the bending strength and the difficulty of reducing the number of wire-adhesive steps, the cost tends to increase.
JP-A-3-87299 (Apr. 12, 1991) has rendered well known an IC card configuration in which an IC module having a very thin LSI ground very thin leaving active elements is fitted in a surface recess.
This conventional configuration is shown in FIG. 4. A semiconductor element 204 is bonded on a substrate 207 by an adhesive 207a. A wiring 208 for connecting semiconductor elements is connected to a conductive pad 202 by way of a through hole 203. This conductive pad 202 is further connected to the wiring on the substrate 207 by conductive paste 201.
The problem of this configuration, as shown in FIG. 4, is that an adhesive layer is in direct contact with the lower surface of the semiconductor element 204 such as a transistor and ionic contaminants easily intrude the semiconductor element, thereby extremely deteriorating the reliability. FIG. 5 is a diagram showing a problem specific to an IC card configured using a thin LSI disclosed in JP-A-3-87299 (Apr. 12, 1991). A thin LSI 41 mounted on a thick card substrate 42 is subjected to tensile or compressive stress on the front and reverse surfaces when the card substrate 42 is bent, thereby exerting a large stress on the LSI chip.
The resulting thin structure and low mechanical strength under a large stress causes the IC to be easily broken by the stress. This gives a rise to a new problem of a considerably reduced reliability.
As described above, the IC card using a thin LSI layer including a thin semiconductor element is easily affected by ionic contaminants. Also, the thinness leads to a low mechanical strength. In the conventional IC cards using a bulk LSI, a bulk IC chip is attached on a thin, easy-to-bend card and wire-bonded. Therefore, the IC is easily broken and is low in reliability. Further, the increased number of packaging steps makes a cost reduction difficult.